UNDERSTANDING PROTEIN KINASE PDK1 REGULATION USING SMALL MOLECULES TARGETING DIFFERENT SITES

SACERDOTI M; PASTOR-FLORES D; RILEY A; SUESS E; BIONDI RM; FROESE K; BAUER A; CZIER G; GROSS LZF; SCHULZE JO; HERBRAND A; POTTER B; LEROUX AE

Salta

Congreso; LV Reunión Científica anual SAIB y XIV congreso de PABMB; 2019

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Overactivation of the phosphoinositide 3-kinase (PI3K) pathway is one of the most frequent events in cancer, a disease that is becoming increasingly frequent because of the increase in life expectancy. A key PI3K downstream event is the phosphorylation of PKB/Akt, S6K, SGK and RSK by master kinase phosphoinositide-dependent protein kinase-1 (PDK1), which also phosphorylates other protein kinases constitutively. Throughout the years we have investigated different mechanisms used by PDK1 to specifically and timely phosphorylate its substrates. Phosphorylation of most substrates, like S6K, SGK, PKC, PRK/PKN, relies on a docking interaction where a C-terminal hydrophobic motif (HM) interacts with a regulatory site, PIF-pocket, located on the small lobe of the kinase domain of PDK1. Since some substrates interact better with PDK1 when their HM is phosphorylated, this acts as a regulated docking interaction. In addition, the interaction with the PIF-pocket allosterically ?activates? PDK1 itself, stabilizing a closed-active structure of the catalytic domain.We have described in the past that the binding of the HM or small compounds to the PIF-pocket allosterically affects the ATP-binding site. Allostery implies that the reverse modulation, i.e. from the ATP-binding site to the regulatory PIF-pocket, should also be possible. Indeed, we have shown that small molecules and metabolites binding at the ATP-binding site can inhibit or enhance the docking interaction at the PIF-pocket. This is important for the mechanism of action of drugs.Interestingly, the interaction with the PIF-pocket of PDK1 is not a requirement for the phosphorylation of PKB/Akt after PI3K activation. Although the HM of PKB/Akt does interact with the PIF-pocket of PDK1, we believe that other mechanisms must regulate that interaction. PDK1 has been described to dimerize. We will here provide preliminary data and discuss if dimerization could also be part of the mechanism by which PDK1 phosphorylates its substrates. We describe the effect of different inositol poliphosphorylated molecules and present results of a screening performed in order to find small compounds to regulate dimer formation.